Liquid crystal display devices are widely used owing to their various advantages such as a thin body, power saving, and zero radiation. The working principle of a liquid crystal panel is to encapsulate liquid crystal molecules between two paired substrates, and apply driving voltages to the two substrates to control the rotation directions of the liquid crystal molecules, thereby refracting the light of the backlight to display the screen. The two paired substrates in the liquid crystal panel are a thin film transistor array substrate (usually referred to simply as an array substrate) and a color filter substrate (usually referred to simply as a color film substrate), respectively. The array substrate includes basic structures such as gate lines, gate electrodes, a gate insulating layer, an active layer that is made of a semiconductor material, data lines, source electrodes, drain electrodes, an insulating layer, and pixel electrodes. Gate electrodes, source electrodes, drain electrodes and the active layer constitute thin film transistors (TFTs). Conventional TFTs are usually amorphous silicon TFTs (i.e. the active layer is made of an amorphous silicon material) and low temperature polysilicon TFTs (i.e. the active layer is made of a low temperature polysilicon material). The array substrate including the amorphous silicon TFTs usually requires 3-5 times of photolithographic mask process, and thus has low cost and vigorous competitiveness. The array substrate including the low temperature polysilicon TFTs usually requires 8-9 times of photolithographic mask process, and thus has higher cost.
However, the carrier mobility of the amorphous silicon TFTs is low, which is difficult to meet the requirement of a large-size display panel for a pixel-driven response rate. Therefore, currently the metal-oxide semiconductor (such as Indium Gallium Zinc Oxide (IGZO)) is usually used as a material of the active layer. Since the carrier mobility of the metal-oxide semiconductor is 20 to 30 times of that of the amorphous silicon, the charge and discharge rates of the TFTs to the pixel electrodes may be greatly improved, and thus the response speed of the pixels may be improved, thereby achieving a faster refresh rate. Meanwhile, the line scan rate of pixels is also greatly improved owing to a faster response, which makes an ultra-high resolution possible in a liquid crystal display apparatus.